The invention relates to a control structure for achieving the desired adjusted rotational speed in an adjusting motor of an electric adjustment device for the camshaft of an internal-combustion engine.
A primary demand on an ideal camshaft adjuster is to guarantee the exact retention of a desired adjustable angular position course of the camshaft. However, in reality deviations arise between the desired and actual adjustable angular positions. These deviations are due to mechanical and electrical inertia, as well as the influence of interfering parameters, such as the camshaft torque.
Reducing the deviations from the desired adjustable angular position course of the camshaft leads to a reduction of pollutant emissions and fuel consumption, to an increase of motor output and torque, and also to a reduction of the onboard power load and the high emission values in the startup phase. The latter assumes that the camshaft adjuster can be controlled just before or during the startup of the engine. This challenge can be met only by an electric camshaft adjuster, because hydraulic adjusters cannot function before and during the startup phase due to the lack of lubricating-oil pressure.
One demand on an electrical camshaft adjuster is for minimal energy consumption of the electrical adjusting motor through a corresponding configuration of the controller. The quality of the controlled system is determined by the profiles of the desired-actual adjusted angles of the camshaft. The quality is increased by minimizing the deviations from the desired adjusted angle.
U.S. Pat. No. 5,787,848 B1 discloses a control structure for achieving the desired adjusted rotational speed in an adjusting motor of an electrical adjusting device for the camshaft of an internal-combustion engine. In this publication, the camshaft adjuster has at least one controller, which generates control signals for the adjusting motor from measurement signals of the internal-combustion engine. This publication concerns the control of internal exhaust-gas recirculation by changing the valve control timing. The exhaust-gas recirculation decreases the torque of the internal-combustion engine. To a achieve a torque curve similar to that of an internal-combustion engine without exhaust-gas recirculation, a low-pass filter is provided in the controller, which should prevent the original torque curve from being exceeded or undershot in sections.